Delta T - briefly explained

Decision support indicator for spray conditions in Farmable App

Max Bangen avatar
Written by Max Bangen
Updated over a week ago

Delta T is a measure of atmospheric stability that is commonly used in agriculture to determine the suitability of crop treatments, such as spraying or fertilizers. Delta T is calculated by subtracting the wet bulb temperature from the dry bulb temperature.

Both temperatures can be measured with common weather stations, such as Davis, Sencrop, Metos, and others. To make use of Delta T in Farmable, you must therefore connect a weather station with your farm in Farmable. We will then automatically calculate Delta T for you.

A Delta T value between 2 and 8 (green area) is generally considered to be the optimal range for applying crop treatments. Values outside of this range can result in poor spray coverage, drift, or other issues that can reduce the effectiveness of the treatment or cause environmental harm.

A Delta T value above 8°C is associated with higher temperatures and lower humidity, if lower than 2°C it is related to high relative humidity values. See yellow areas. Above 12 (red area) is considered to be unsuitable.

The chart below relates relative humidity and dry temperature to determine Delta T values. Adapted from Nufarm’s sprays decisions chart.

Keep monitoring Delta T before and during your spray activities to optimize your spray schedule. Weather conditions can change quickly, so having the possibility to monitor Delta T can help make better decisions about crop treatment applications.

It's important to note that Delta T is just one of several factors that influences the performance of sprays and other crop treatments. You should therefore also consider other factors including wind speed, humidity, temperature, and the type of treatment being applied. Also, check with your agronomist in case of doubt.

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